Ion beam lithography for direct patterning of high accuracy large area X-ray elements in gold on membranes

Abstract

X-ray elements like Fresnel zone plates (FZPs) are challenging objects for nanofabrication, as they require high accuracy, high aspect ratio and large area structures. In most cases they are fabricated with electron beam lithography (EBL) based techniques plus plasma or wet etching, which deliver routinely zone plates with outermost zone widths down to 25 nm and aspect ratios of 5:1. In this work we present a complementary resistless technique based on ion beam lithography (IBL) using direct milling with a focused Gallium beam and advanced process control. A zone plate of 100 μm diameter and 100 nm outermost zone widths has been produced in a 500 nm thick gold layer on a Si3N4 membrane. To achieve the desired resolution we developed a 15 h low current milling process including high accuracy automated drift correction on a mark outside the 500 × 500 μm membrane window. In addition first results of X-ray imaging with the zone plate are presented. To the best of our knowledge this is the first ion beam fabricated zone plate which has proven its functionality for X-ray imaging.